Unless otherwise indicated herein, the description provided in this section is not itself prior art to the claims and is not admitted to be prior art by inclusion in this section.
A typical wireless communication system includes one or more base stations, each radiating to define one or more coverage areas, such as cells and cell sectors, in which wireless communication devices (WCDs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped devices, can operate. Further, each base station of the system may then be coupled or communicatively linked with network infrastructure such as a switch and/or a gateway that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a WCD within coverage of the system may thus engage in air interface communication with a base station and thereby communicate via the base station with various remote network entities or with other WCDs served by the system.
In general, a wireless communication system may operate in accordance with a particular air interface protocol or radio access technology, with communications from a base station to WCDs defining a downlink or forward link and communications from the WCDs to the base station defining an uplink or reverse link. Examples of existing air interface protocols include, without limitation, Orthogonal Frequency Division Multiple Access (OFDMA) (e.g., Long Term Evolution (LTE) or Wireless Interoperability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), Global System for Mobile Communication (GSM), WI-FI, and BLUETOOTH. Each protocol may define its own procedures for registration of WCDs, initiation of communications, handover between coverage areas, and functions related to air interface communication.
In accordance with the air interface protocol, each of the one or more coverage areas of such a system may operate on one or more carrier frequencies and may define a number of air interface channels for carrying information between the base station and WCDs. By way of example, each coverage area may define a pilot channel, reference channel or other resource on which the base station may broadcast a pilot signal, reference signal, or the like that WCDs may detect as an indication of coverage and may measure to evaluate coverage strength. Further, each coverage area may define a downlink control channel for carrying system information, page messages, and other control signaling from the base station to WCDs, and an uplink control channel for carrying service requests and other control signaling from WCDs to the base station, and each coverage area may define downlink and uplink traffic channels or the like for carrying bearer traffic between the base station and WCDs.
When a WCD initially enters into coverage of a wireless communication system (e.g., powers on in coverage of the system), the WCD may detect a reference signal and read system information broadcast from a base station and may engage in a process to register itself to be served by the base station and generally by the system. For instance, the WCD may transmit an attach message on an uplink control channel to the base station, and the base station and/or supporting infrastructure may then responsively authenticate and authorize the WCD for service, establish a record indicating where in the system the WCD is operating, establish local profile or context records for the UE, and provide an attach accept message to the WCD. Thereafter, the WCD may then be served by the system in an idle mode or a connected/active mode. In the idle mode, the WCD may monitor a downlink control channel to detect page messages and other information regarding incoming communications and may similarly transmit uplink control signaling to initiate communications or for other reasons. In the connected/active mode, the WCD may have particular traffic channel resources assigned by the RAN, which the WCD may use to engage in communication of bearer traffic and the like.
When a WCD is served in a particular base station coverage area, the WCD may also regularly monitor the reference signal strength in that coverage area and in other coverage areas of the system, in an effort to ensure that the WCD operates in the best (e.g., strongest) coverage area. If the WCD detects threshold weak coverage from its serving coverage area and sufficiently strong coverage from another coverage area, the WCD may then engage in a handover process by which the WCD transitions to be served by the other coverage area. In the idle mode, the WCD may do this autonomously and might re-register in the new coverage area. Whereas, in the connected/active mode, the WCD may report signal strengths to its serving base station when certain thresholds are met, and the base station and/or supporting infrastructure may work to hand the WCD over to another coverage area.
Further, when a WCD is served by a base station in the connected/active mode, the WCD and base station may engage in a power control process to help manage the transmission power that the WCD uses for its transmissions to the base station. For example, the WCD may transmit to the base station at a particular transmission power level, and the base station may receive the WCD transmissions and compare a quality (e.g., signal strength or signal-to-noise ratio) of the received transmissions with a defined set point. If the base station thereby determines that the receive quality falls below the set point, then the base station may transmit to the WCD a power-up command to cause the WCD to incrementally increase its transmission power. Whereas, if the base station determines that the receive quality falls above the set point, then the base station may transmit to the WCD a power-down command to cause the WCD to incrementally decrease its transmission power. Meanwhile, the base station may also dynamically adjust the set point based on an evaluation of error level (e.g., frame error rate or bit error rate) in the received WCD transmissions, in an effort to ensure that the set point will be a good benchmark for the power control process to keep transmission errors within a tolerable level.